Gear-driven trimming potentiometer

ABSTRACT

A trimming potentiometer comprising a base with a flange extending perpendicular to it and a cover that encloses the flange and is sealed to the base. Supported on the flange is an assembly comprising a post, a non-conductive plate on which an arcuate resistive path is disposed, a contact plate with a contact finger that presses against the resistive element, and a gear journaled on the shaft and releasably coupled to the plate to move the finger along the arcuate resistive path. The shaft, the plate and finger, and the gear are joined together, and a spring is provided to force the plate into engagement with the gear. The cover has a lead screw mounted in it with a head available to the outside and the threaded portion in mesh with the gear. The axial direction of the screw may be either perpendicular to the base or parallel with it.

United States Patent Mulqueen et al.

[15] 3,676,824 1 July 11, 1972 [54] GEAR-DRIVEN TRIMMING POTENTIOMETER [72] Inventors: John J. Mulqueen, Hopatcong; Edward Schoettly, Madison, both of NJ,

abandoned.

[52] US. Cl. ..338/162, 338/DIG. l [5 1] Int. Cl ..H0lc 9/02 [58] Field ofSearch ..338/DIG. l, 180, 181, 162;

[56] References Cited UNITED STATES PATENTS 8/1965 Mathison ..338/DIG. 1

3,522,572 8/1970 Michik et al. ..338/DIG. 1

Primary Examiner-Lewis H. Myers Assistant Examiner-D. A. Tone Att0rney-Thomas M. Ferrill, Jr. and Roger Norman Coe [57] ABSTRACT A trimming potentiometer comprising a base with a flange extending perpendicular to it and a cover that encloses the flange and is sealed to the base. Supported on the flange is an assembly comprising a post, a non-conductive plate on which an arcuate resistive path is disposed, a contact plate with a contact finger that presses against the resistive element, and a gear joumaled on the shaft and releasably coupled to the plate to move the finger along the arcuate resistive path. The shaft, the plate and finger, and the gear are joined together, and a spring is provided to force the plate into engagement with the gear. The cover has a lead screw mounted in it with a head available to the outside and the threaded portion in mesh with the gear. The axial direction of the screw may be either perpendicular to the base or parallel with it.

6 Claims, 6 Drawing Figures Patented July 11, 1972 3,676,824

3 Sheets-Sheet 1 FIG. 2

INVENTORS JOHN 1r. MULQUEEN BY jWARD w. SCHOETTLY ATTORNEY Patented July 11, 1972- 5 Sheets-Sheet 2 Patented July 11, 1972 3,676,824

5 Sheets-Sheet 5 FIG. 5

74 74 (so g5 I! l 7| we 76 77 L I 1 57 FIG. 6 72 I66 l6l INVENTOR. JOHN J. MULQUEEN EDWARD W. SCHOETTLY TQM/w ATTORNEY GEAR-DRIVEN TRIMMING POTENTIOMETER CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part application of Ser. No. 7,5 62, filed Feb. 2, 1970, now abandoned.

FIELD OF THE INVENTION This invention relates to small potentiometers such as may be used for trimming purposes and which are provided with an adjustment screw to permit multi-turn operation for precise control and with a resistive element laid out along an arcuate path to permit the potentiometer to be assembled in a compact, substantially square box as opposed to an elongated container. Such potentiometers are normally referred to as square trimming potentiometers.

BACKGROUND OF THE INVENTION In recent years trimming potentiometers have become quite important because of their capacity to provide exact control of the resistance in electronic circuits where a precise resistance is required but where the resistance value need not be changed once the proper value is obtained. One configuration of such a potentiometer is in the form of an elongated enclosure with the'resistance element in the form of a flat, straight strip of resistive material. In such potentiometers a lead screw is provided to drive a contact along the length of the resistive element and additional means are provided to establish connection to the contact at every point along its range of travel. However, such elongated potentiometers are not always convenient to use because of the amount of space that they occu- P)- To minimize the amount of space required, another form of trimming potentiometer has been developed in which the resistive element is formed into an are which may be half of a circle or more. The total length of the resistive path can be quite long if it is so formed but the overall maximum dimensions of the potentiometer may be substantially less than the greatest dimension of a linear potentiometer having a comparable resistive path length laid out in a straight line. The contact is moved along the resistive path by a gear drivenby a lead screw to make it easier to adjust the setting of the contact precisely. Not only is there a limit to the total amount of space that the potentiometer can be allowed to occupy, but the position of the lead screw and the locations of the terminals may be dependent on the layout of the apparatus in which the potentiometer is used. Several different configurations of such potentiometers have been produced. In one configuration there are leads, which may be in the form of rigid posts, extending from one side of the potentiometer with the axial direction of the lead screw parallel to those leads or posts. In another configuration the axial dimensions of the lead screw may be perpendicular to the support posts.

Potentiometers of the square type are usually made quite small and may have major external dimensions of the order of one-fourth of an inch. Such small components cannot be very strong, and means must be provided to keep them from being broken if a user attempts to turn the lead screw beyond a position that will bring the contact against a mechanical stop that limits the range of travel of the contact.

SUMMARY OF THE INVENTION It is one of the principal objects of the present invention to provide a simplified structure for a square trimming potentiometer and an internal sub-assembly that can be inserted into a cover in which the lead screw may be mounted so as to be either perpendicular to or parallel with the terminals.

Another object is to provide a square trimming potentiometer with an improved overriding clutch arrangement between the lead screw and the contact to prevent the device from being damaged by rotation of the lead screw beyond a predetermined stop.

The gear-driven trimming potentiometer of the present invention embodies a base and a plate, attached to the base, which contains an arcuate resistive element. A gear journaled on a shaft is employed to move a contact finger or contact fingers along the arcuate resistive element.

In the present invention the contact finger or fingers may be provided with or attached to, a plate that intercepts a fixed stop at each end of the range of travel of the finger or fingers so that the gear can continue to turn as long as a user persists in rotation of the lead screw. The plate and the gear may both be mounted, in accordance with the present invention, on a support post, and resilient means may be mounted on the same post to force the plate and gear into engagement, but in such a way that the force of the resilient means may be over,- come if an attempt is made to rotate the lead screw beyond the point at which the plate engages the stop.

BRIEF DESCRIPTION OF THE DRAWINGS Other and further objects, advantages, and features of the invention will be apparent to those skilled in the art from the following detailed description thereof, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a plan view of part of the internal assembly of potentiometer constructed according to the present invention;

FIG. 2 is a side cross-sectional view along the line 2-2 of the components in FIG. 1;

FIG. 3 is a cross-sectional view of a complete potentiometer including the assembly of FIGS. 1 and 2;

FIG. 4 is a cross-sectional view of one cover that may be used with the subassembly of FIGS. 1 and 2 to form a complete potentiometer;

FIG. 5 is an end view of the cover in FIG. 4; and

FIG. 6 is a cross-sectional view of a different embodiment of a cover for the potentiometer.

PREFERRED EMBODIMENTS The subassembly shown in FIGS. 1 and 2 comprises an insulating support plate 11 of a suitable material, such as 96 percent alumina, on which two gold contact pads 12 and 13 have been placed along with an arcuate film of resistive material 14 that covers an arc of about 290 and makes good electrical contact at each end with the pads 12 and 13. The plate 11 is placed in contact with a flat support plate 16 that extends from, and in the present embodiment is integral with, a base 17. The base includes a plurality of channels including the channel 18 through which terminal pins 19-21 are inserted. Each of the terminal pins has a bent-over head 23-25, respectively, to serve as stops that prevent the terminal pins from being pulled out of the base and also to serve as connection terminals for attachment to a jumper in the form of a flat metal tab. The first of these jumpers is indicated by reference numeral 27 and is welded to the head 23 of the terminal 19 and to the terminal pad 13. The second jumper 28 is welded to the head 24 of the terminal 20 and extends along a channel 29 in the plate 16 to a hole 31 where, initially during the manufacture of the potentiometer, it is not attached to anything. The hole 31 actually has a slot 32 along one side through the jumper 28 passes. The third jumper 33 is attached to the head 25 of the terminal 21 and to the pad 12. The base 17 has an integ'ral stop 34 centrally located and having an arcuate surface substantially concentric with the arc of the resistive element 14. The stop 34 has abutment edges 36-37. The base 17 also has a peripheral flange 38 that extends outwardly beyond the main portion of the base a short distance.

FIG13 shows the elements of FIG. 2 with additional parts to make up a complete potentiometer. A post 39 extends into the hole 31 in the plate 16, although it is not necessarily tightly fitted into the hole. The jumper 28 is welded directly to the end of the post 39, and one reason for the hole 31 is to give access of the end of the post to permit the jumper to be welded to it. The post 39 has an outwardly extending flange 41 that abuts against the side of the plate 11 away from the plate 16.

An annular disc 42 is threaded on to the post 39 on the other side of the flange 41 from the plate 11. The central aperture of the disc 42 may be somewhat larger than the post 39 to permit the disc to rotate easily with respect to the post. The disc 42 has several crimped projections 44 evenly spaced around its perimeter to engage matching notches 46 in a flange that forms one surface of a gear 47. The surface containing the notches 46 may also extend beyond the teeth 48 of the gear to form a flange. Near the opposite end of the post 39 from the jumper is a groove 49 with which a lock washer 51 may engage to hold the gear 47 on the post.

The metal disc 42 has contact finger 52 welded to it. The end of the finger 52 is divided into separate sections 53 by short cuts in the finger. Electrical contact from the plate 42 to the post 39 is provided by a annular metal spring 54 that encircles the post 39 and presses firmly and resiliently against the disc 42 and against the facing surface of the flange 41. In addi- .tion to some electrical contact between the disc 42 and the post 39, the spring 54 provides axial resilient force that presses the crimped projections 44 of the disc 42 into engagement with the matching notches 46 in the gear 47 so that rotation of the gear will result in rotation of the disc 42 and therefore of the contact finger 52.

It is one of the features of the present invention that the foregoing elements can be assembled and tested as a separate sub-assembly for later assembly with a cover and lead screw to form a complete potentiometer. FIG. 3 shows one form of cover 56 that has sides 57 and 58 along with other sides 59 and 60 (not shown) and a top 61 that completely encloses the moving components of the potentiometer. The edges of the sides 57-60 fit down over the base 17 and can be cemented to the flange 38 by a suitable material such as an epoxy resin 63. The cover 56 has a lead screw 64 which is captive therein. As may be seen, the head 65 of the lead screw extends from the top 61 so that the axis of the lead screw is parallel to the terminals 19-21.

The cover 56 and the lead screw 64 are assembled as a separate unit before being joined to the base and the elements mounted thereon. FIGS. 4 and show the cover and lead screw in greater detail. As may be seenlin FIG. 4, the lead screw 64 extends through a circular opening 66 in one corner of the top 61. The lead screw has a cylindrical portion 67 that fits within this opening and a threaded portion 68 within the confines of the cover 56. Between the cylinder portion 67 and the threaded portion 68 is a reducing diameter section 69 around which a nylon snap ring 71 is placed prior to assembly. The nylon ring 71 has a natural outer diameter larger than the diameter of the opening 66, but a section of the ring is cut out so that the ring can be compressed enough to fit in this opening. In addition, the nylon ring is shaped so that the end that enters the opening 66 first is rounded and the outer surface of the ring is tapered to facilitate entry into the opening. The other side of the ring 71 is squared off to prevent the ring from being compressed and pulled back through the opening after it has been inserted. In order to minimize the entry of moisture or other contaminates into the cover 56, an O-ring 72 encircles the cylindrical portion 67 of the lead screw and fits within a recess 73 in the top 61. The cover 56 has an internal U- shaped shelf 74 that helps to support the flange forming one surface of gear 47 (FIG. 3). In addition, the inner surface of the side 57 of the cover 56 has a projecting portion 76 with a circular part 77 that helps to support one end of it.

Sometimes it is desirable for the adjustment screw 64 to be positioned so that its axis is perpendicular to the longitudinal direction of the terminals 19-21. Such a modification is shown in the cover of FIG. 6 which corresponds to the cover shown in FIGS. 4 and 5, except that the screw has been moved 90". This makes certain other changes possible in the internal construction of the cover 156 in FIG. 6.

The cover 156 in FIG. 6 includes sides 157, 159 and 160 and a top 161. The side 160 is provided with an aperture 166 through which the shank of the screw 64 is inserted. This screw is identical with that in FIG. 4 but held in place not by a snap ring as shown in FIG. 4 but by a small quantity of potting compound 171. This compound may be an epoxy resin which can be inserted in place in a recess in the cover 156, as shown. A hypodermic needle can be used for the purpose, especially with those potentiometers in which the major dimension is of the order of one-quarter inch. By first applying a small amount of mold release to the neck, or reduced diameter portion 69 of the screw 64, the resin 171 will not adhere to it but will adhere to the fixed part of the cover 156 and will prevent the screw from falling out. The potting compound 171 also helps to seal the inner part of the potentiometer from having air get in by way of the screw 64, although it may still be desirable to provide an O-ring 72 as in the embodiment in FIG. 4. It is possible, of course, to use the same snap ring for a retainer of the screw 64 as was used in the embodiment in FIG. 4, but the configuration of the cover 156 in FIG. 6 facilitates direct application of the epoxy resin to the retaining area. The cover 156 also permits a complete half-circle journal 177 to be formed in the molded wall 157, whereas the structure of the cover 56 in FIG. 4 cannot easily include a semi-circular journal.

In assembly the cover 156 of FIG. 6 with the base 17 and elements mounted thereon as shown in FIG. 3 the cover 156 need only be pressed into place with, at most, a slight turning of the screw 64 to mesh with the gear teeth 48 of FIG. 3. This is an advantage over the cover 56 shown in FIG. 4 because, in the cover 56 the direction of engagement of the screw 64 with the gear teeth 48 is such that the gear 47 may have to turn a substantial part of a revolution. The teeth 48 feed into engagement with the thread 68 of the screw. In some cases, pressing the cover 56 of FIG. 4 onto the basic structure of FIG. 3 may necessitate turning the screw 64 several turns or, at least, exercising some care to make sure that the disc 42 will not be in position to be driven up against the stop 36 or 37 (FIG. 1) as the cover is pressed into place.

The exact composition of the contacts or fingers in the above embodiments is not critical. Preferably the contacts or fingers which are in engagement with the resistive film strip are made from precious metal alloys. The metal alloy employed should be selected to provide reasonable wear resistance characteristics and also provide excellent electrical contact. An example of a precious metal alloy which may be used is an alloy having the following composition:

Palladium 35% Silver 30% Copper 1 3.75% Platinum 10% Gold [0% Zinc l .25%

Another suitable precious metal alloy has the following composition:

Gold 56.25% Copper 21% Palladium l0.5% Silver 5.25% Nickel 5.25% Zinc 1.75%

While FIG. 3 shows multiple fingers or contact elements for engaging the resistive film strip, it will be understood that the number of contact elements or fingers is not critical.

It will also be understood that it is not essential that the resistive metal film element have separate conductive pads electrically connected to the ends of the element. The conductive pads may be an integral part of the resistance element.

From the foregoing it will be seen that this invention is well adapted to obtain all of the ends and objects herein above set forth, together with other advantages which are obvious and which are inherent to the system.

It will be understood that changes may be made in the details of construction and arrangement of parts, shown and described herein, without departing from the spirit of the invention as set forth in the accompanying claims, as the preferred forms of the invention have been given by way of illustration only.

What is claimed is:

1. A potentiometer comprising:

a. a sub-assembly comprising a support plate, an arcuate resistive element disposed on said plate, and a base attached to said support plate;

b. a plurality of terminals mechanically attached to said subassembly and electrically connected to said resistive element;

c. a pivotally mounted conductive member comprising a stop;

d. a contact connected to said conductive member to be moved thereby along the arcuate length of said resistive element;

e. a pivotally mounted driving member concentric with said pivotally mounted conductive member;

f. sliding contact means from one of said terminals to said contact;

g. a plurality of projections on one of said pivotal mounted members and a plurality of recesses on the other of said pivotally mounted members engageable with said projections, and resilient means urging said projections and said recesses into engagement whereby rotation of said driving member rotates said conductive member; and

h. fixed stop means to engage said stop on said conductive member to limit the rotational movement thereof,

wherein said driving member is a pinion gear and said subassembly comprises a post concentric with said resistive element and perpendicular to said support plate, said gear and said conductive member being pivotally mounted on said post, and wherein a cover comprising sides and a top are present, said sides being joined to said base to engage said support plate, said conductive member, and said pinion gear, and wherein a worm gear rotatably mounted in said cover engaging said pinion gear to rotate said pinion gear in response to rotation of said worm gear is present, and wherein said worm gear has a groove in the portion thereof within said cover, said potentiometer comprising, in addition: a split retaining ring held within said groove, the normal diameter of said ring being larger than the diameter of said worm gear.

2. The potentiometer of claim 1, in which said worm gear has an axis substantially perpendicular to said base.

3. The potentiometer of claim 1, in which said worm gear has an axis substantially parallel to said base and to said support plate.

4. The potentiometer of claim 1 wherein the terminals are electrically connected to the resistive element by means of flat metal jumpers.

5. A potentiometer comprising:

a. a sub-assembly comprising a support plate, an arcuate resistive element disposed on said plate, and a base attached to said support plate;

b. a plurality of terminals mechanically attached to said subassembly and electrically connected to said resistive element;

. a pivotally mounted conductive member comprising a stop;

d. a contact connected to said conductive member to be moved thereby along the arcuate length of said resistive element;

e. a pivotally mounted driving member concentric with said pivotally mounted conductive member;

f. sliding contact means from one of said tenninals to said contact;

g. a plurality of projections on one of said pivotal mounted members and a plurality of recesses on the other of said pivotally mounted members engageable with said projections, and resilient means urging said projections and said recesses into engagement whereby rotation of said driving member rotates said conductive member; and h. fixed stop means to engage said stop on said conductive 

1. A potentiometer comprising: a. a sub-assembly comprising a support plate, an arcuate resistive element disposed on said plate, and a base attached to said support plate; b. a plurality of terminals mechanically attached to said subassembly and electrically connected to said resistive element; c. a pivotally mounted conductive member comprising a stop; d. a contact connected to said conductive member to be moved thereby along the arcuate length of said resistive element; e. a pivotally mounted driving member concentric with said pivotally mounted conductive member; f. sliding contact means from one of said terminals to said contact; g. a plurality of projections on one of said pivotal mounted members and a plurality of recesses on the other of said pivotally mounted members engageable with said projections, and resilient means urging said projections and said recesses into engagement whereby rotation of said driving member rotates said conductive member; and h. fixed stop means to engage said stop on said conductive member to limit the rotational movement thereof, wherein said driving member is a pinion gear and said subassembly comprises a post concentric with said resistive element and perpendicular to said support plate, said gear and said conductive member being pivotally mounted on said post, and wherein a cover comprising sides and a top are present, said sides being joined to said base to engage said support plate, said conductive member, and said pinion gear, and wherein a worm gear rotatably mounted in said cover engaging said pinion gear to rotate said pinion gear in response to rotation of said worm gear is present, and wherein said worm gear has a groove in the portion thereof within said cover, said potentiometer comprising, in addition: a split retaining ring held within said groove, the normal diameter of said ring being larger than the diameter of said worm gear.
 2. The potentiometer of claim 1, in which said worm gear has an axis substantially perpendicular to said base.
 3. The potentiometer of claim 1, in which said worm gear has an axis substantially parallel to said base and to said support plate.
 4. The potentiometer of claim 1 wherein the terminals are electrically connected to the resistive element by means of flat metal jumpeRs.
 5. A potentiometer comprising: a. a sub-assembly comprising a support plate, an arcuate resistive element disposed on said plate, and a base attached to said support plate; b. a plurality of terminals mechanically attached to said sub-assembly and electrically connected to said resistive element; c. a pivotally mounted conductive member comprising a stop; d. a contact connected to said conductive member to be moved thereby along the arcuate length of said resistive element; e. a pivotally mounted driving member concentric with said pivotally mounted conductive member; f. sliding contact means from one of said terminals to said contact; g. a plurality of projections on one of said pivotal mounted members and a plurality of recesses on the other of said pivotally mounted members engageable with said projections, and resilient means urging said projections and said recesses into engagement whereby rotation of said driving member rotates said conductive member; and h. fixed stop means to engage said stop on said conductive member to limit the rotational movement thereof; wherein said driving member is a pinion gear which is rotated in response to rotation by a worm gear and wherein said worm gear has a groove inside the potentiometer and potting compound present within said groove retains said worm gear in said potentiometer.
 6. The potentiometer of claim 5 wherein the plurality of terminals mechanically attached to said sub-assembly and electrically connected to said resistive element is by means of flat metal jumpers. 